Box Tree Moth & CaterpillarHow did it get here?

Learn about the history andreasons behind how thepest has ended up in the

UK.

Where is it?

A map updated with datafrom gardeners and

enthusiast around thecountry will let you know ifthere is moth or caterpillarin your area and how bad it

is.

What Can I Do?

Learn how to deal with andeliminate the hungry

critters.

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Quick Summary

The moth lays pale yellow eggs on the underside of box leaves

EBTS UKEuropean Boxwood & Topiary Society

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When the eggs hatch the greenish yellow caterpillars eats the leaves and produces acobwebbing & a trail of pellets in it’s wake

Caterpillars can survive over winter down to -30c

Becomes a pupae in a chysalis before emerging as a white semi-transparent moth

The season for Cydalima perspectalis is from late March to the end October

In the UK 3-4 life cycles each per year depending on temperature, these last around 45days

Preferred temperature 21-33c

Box moth can fly 10km/year

Box trees can survive being attacked as long as the larvae don’t eat the bark of the mainstems

In Northern Europe, the caterpillars have no natural predators that control their spreadas they have toxins in them that taste bad to birds and other animals

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How Did It Get Here?

The Pests Impact

Since 2007 box moth caterpillars have been devastating parterresand other topiary in domestic, commercial and historic gardensacross Europe. However, the impact is not just in gardens. Thecaterpillar is decimating large areas of Europe’s natural boxwoodlands. The Northern Caucasus as well as Bulgaria, NW Italy,Romania and southern France have all been badly affected. In theUK wild box is now under threat with small infestations reported atBox Hill, though currently no reports at other large areas of naturalbox such as the Chilterns.

Wild Box – TarnValley, France

Wild Box – TarnValley France

The severity of the infestations is demonstrated dramatically inGermany’s Grenzarch-Whylen Nature Reserve which contains thecountry’s largest box tree forest. Between 2009 and 2010, thecaterpillars attacked all the box trees causing more than 90% de-foliation and 27% lost all their leaves. Although the population ofmoths then decreased, having eaten most of its food source, by2012 the trees that had been fully defoliated died as their bark hadalso been eaten and thus exposed the trees to fungal infection. Observations show the eco-system in the forest is beginning tochange with new ground cover taking the place of the B.sempervirens which will likely now only remain in smaller clumps.[1]

Where did the pest come from?

The origin of the moth is recorded as North China, but it has spread a long way since 1859when it was first identified and now covers large areas of the continent of Europe.

The consensus is that the wide scale spread is not caused by the flight of the moths, but bycommercial movement of infected plants where leaves are carrying undetected eggs. Anexample of this was at the 2012 Sochi Winter Olympic Games. During the build-up, Italianbox was imported for planting in the Olympic village where Russian experts then foundCydalima perspectalis in the site. Control measures using Aktelik, a non-systemicorganophosphorus insectoacaricide product with enteric-contact action, failed, resulting ina rapid spread into the natural boxwood in the territory of yew-box grove in the CaucasianBiosphere Reserve. It has since spread further across Georgia and where all the Buxusplants have suffered from the caterpillar. Damage has also been observed on Rubus spp.,Ruscus colchicus, Ruscus fruticosus and Smilax excelsa. [2]

Map data from ‘Cydalima perspectalis (Walker, 1859) (Leipidoptera, cranambidae) and thethreats for the nature 2000 habitat 5110 in Liguria (NW Italy)’

Box Moth were first categorised as Cydalima perspectalis in 1859 byFrancis Walker (1809-1874) when he was working for the BritishMuseum collating their specimens. They were recorded in the Listof the specimens of lepidopterous insects in the collection of theBritish Museum. Without the aid of modern technology to cross-reference specimens, Walker gave it more than one name, so boxmoth was also called Phakellura perspectalis, Diaphaniaperspectalis and Glyphodes perspectalis.

Francis Walker(1809-1874)Wikipedia

Life Cycle

This lasts around 45 days depending on temperature and light levels as each stagerequires a number of degree days (a value based on hours of sunlight and temperature).

By Cosmin Manci –Shutterstock.com

# Eggs – 0.8-1.0mm diameter are laid on the underside ofleaves in a flat sheet and coloured greenish yellow at firstwith black dots appearing as the larval head capsule isformed.

Temperature threshold for egg development >10.9c

By Zerbor –Shutterstock.com

# Caterpillars/Larvae – When they hatch are greenish yellowin colour, developing black heads and light & dark stripswith spots along their length as they grow. Fully grownthey are about 4cm long, living for about 2 weeks.

Temperature threshold for this state is >8.4c

By Cosmin Manci-Shutterstock.com

# Pupae/Chrysalis – The pupae are cocooned in whitewebbing spun around leaves and are between 1.5-2.0cmlong.Temperature threshold for this state is >11.5c

# Moths – Have a wing span of about 4cm and either has athick dark brown border around a white coloured wingwith distinctive dots halfway down the leading edge of thewings (common variant) or less commonly the wings arealmost entirely brown with white dots (Melanic variant). The moths start laying eggs 2-3 days after they startflying.

By vvoe – Shutterstock.com

# In Central & South Europe, the life cycle of C. Perspectalisis repeated three and sometimes four depending on thecombination of temperature and light as they need aspecific number of ‘degree days’ for each stage of theircycle. When the day-length drops below about 13.5hrs thelarvae will ‘diapause’ (the dormant stage of a developinginsect) so that it can overwinter in a web spun on Buxusleaves. In this state, it can survive temperatures down to-30c. In spring it will come out of diapause and continueit’s development, eating the new box leaves, beforechanging into the pupae stage.

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What Can I Do?

Quick Guide

If your box bushes havebeen attacked by thecaterpillars, just followthese instructions and yourplants will almost certainlygrow back again.

Spray your plants with a biological insecticide (see listbelow) or if you don’t like using sprays pick off theremaining caterpillars by hand (kill them off bydropping them in a jar of water with few drops ofwashing up liquid in it)

Carefully comb through the plants with a small handclaw/rake to remove the cob-webbing and green ballsof frass and clear away the debris under the plants –sometimes easiest to put a cloth under the plant tocatch the debris

Water the plants at their base, avoiding wetting theleaves as this can cause the conditions that allowblight to take hold

EBTS UK does not recommended using a pressurehose/jet wash to remove caterpillars/debris as itwill cause damage to the plants and could causethe conditions for blight

Keep your eyes peeled for any returning caterpillarsand re-spray as necessary

Setup a pheromone trap (see details below) to catchthe male moths thus reducing the number of fertilisedeggs that get laid by the females

Getting Rid Of The Moths

Pheromones

Pheromone traps have tended to be used in scientificresearch for recording numbers of specific insects. Theywork by using a lure impregnated with a syntheticpheromone of the female insect to entice the male into atrap so that numbers can be assessed. The RHS website,under ‘Non chemical control’ measures, only suggests trapsbe used for monitoring adult activity. However,experiments in France as part of the SaveBuxus project(2014-18) have looked at their use as a control measure, onthe basis that trapping the males reduces the number offertilised eggs and thus disrupts the breeding cycle. So far,their research has established that the funnel-type trap isthe most effective design for catching male box moths. Other types such as sticky traps, where the moths becomestuck to a surface, need replacing to regularly to beeffective in high pressure infestations. They also testeddifferent lure types which come in a variety of forms fromimpregnated rubber tips, plastic vials to a thick sticky liquid– all work in the same way by slowly defusing the syntheticpheromone. Different lures last for differing times with theearlier forms lasting from five to six weeks whilst the latestdesigns can last up to eight months before the pheromone isdepleted and needs to be replaced.

Sticky gel in a syringe

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Impregnated rubber bung

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New long life vial

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Example of apheromone trapfrom Bayer the

BuxaTrap

In a test over a 5km2 area of the Val-de-Marne rose garden, outsideParis, which has large amounts of box hedging round it’s rose beds,50 BUXatrap® traps equipped with GinkoBuxus lures were arrangedwith a trap per 100 m². This showed there were only 23% ofcaterpillar’s present compared to the control area, similar resultswere found in the other test sites at Castle Park of Champs-sur-Marne, Vieux Moulin, Gradignan & Château Haut-Brion in Pessac.However, just using the pheromone traps didn’t protect the rosegarden and in Autumn 2016 the boxwood was totally defoliated.

A new version of the Ginko Buxus lure produced by Sumi Agro wasreleased in 2017 which use the same pheromone used in earlierversions but has a slow release mechanism that make it effectivefor eight months. This means you don’t have to remember tochange the lures during the season making it much easier for usersas they then only have to empty the traps. The lures are widelyavailable in France but are not currently easy to purchaseelsewhere (it is now available in the UK from greengardener.co.ukfollowing work by EBTS UK to connect the makers with retailers).

Pheromone traps are a useful tool in reducing the box moth problemand should be used in conjunction with spraying or biologicalcontrols.

Setting up a pheromone trap

Emptying a pheromone trap

Buy Long Life Pheromone Lures fromGreenGardener.co.uk

Getting Rid Of TheCaterpillarsBiological insecticide

Most reports consider Bacillus thuringiensis (Bt) to be the best option for killing box treecaterpillars as they stop eating within an hour of ingesting a treated leaf. The USEnvironment Protection Agency has not found any human health hazards and has no knowneffect on wildlife such as mammals, birds, and fish. In some countries, including Australia,Canada and the USA a number of products have organic certification. [5]

XenTari & Dipel are both based on the Bt bacterium which contains protein endotoxincrystals and living spores. There are fifty subspecies, the most commonly used forcaterpillars are subsp. Kurstaki (in Dipel) & aizawai (in XenTari). When the targeted insecteats a treated leaf, the toxins dissolve in the high pH of the pest’s stomach, causing holesin the lining which allow the spores into the gut. These then germinate causing the deathof the insect within a couple of days.

Spray plants as soon as caterpillars are spotted. Bt doesn’t stay active on leaves for morethan ten days as it breaks down under UV light and needs to be ingested to work.

Note: Currently Bt based products are not registered for domestic use in the UK, they areavailable to professionals.

Chemical Insecticide

There are a large range of different types of chemical insecticides available from gardencentres, though many are not safe to use around bees, fish and other garden beneficialinsects – so always read the instructions carefully before use.

Pyrethrum based products…

Py Spray Garden Insect Killer

Bug Clear Gun for Fruit and Veg

Defenders Bug Killer

Growing Success Fruit & Veg BugKiller

Growing Success Shrub & FlowerBug Killer

Deltamethrin based products suchas…

Bayer PROVADO Ultimate BugKiller

Bayer Sprayday Greenfly Killer

Lambda-cyhalothrin products suchas…

Westland Resolva Bug Killer

Note: Make sure you treat the affected area thoroughly and be careful not to spray whilstplants are flowering so you don’t affect bees and insects that are pollinating the plants. This is best done during still weather, preferably in the morning before insects becomeactive.

Nematodes

These are small worms that are supplied as a powder that is mix with water and apply witha watering can or hose attachment and repeated 2 more times at 7 day intervals. Thenematodes need to be sprayed directly onto the caterpillars as they work by contact. Itkills by entering through natural openings in the bodies of the larvae and producing bacteriathat disrupts their digestive system. Having made contact they then reproduce in the deadcaterpillars and spreading to others until they have nothing left to eat, at which point theydie. However they also die if the surroundings aren’t moist or the temperature drops below12c. As nematodes are a live product they can only be stored for a maximum of 4 weeksand must be kept in a refrigerator during this time. They can be very effective if applied atthe right time.

Use a Professional?

Professional spraying can be done using pesticides such as DECIS (active ingredient:deltamethrin) which lasts for around 5-6 weeks and is in a stronger concentrations than isavailable to domestic gardeners (needs to be used with care around bees).

Search Google for suitably qualified professional in your area.

Prospects for the Future

Here are some of the current things in development that haven’t yet made it tocommercial products or are just becoming available on the market in the UK.

Essential Oils & Plant Extracts

In her dissertation, Stefanie Gabriele Göttig, details tests that were carried out using sixplant extracts, seven essential oils and one seed oil.[3] The tests looked at the repellenteffect of different concentration of the extracts and oils when applied to Buxus leavesand therefore the number of egg laid by the female moths. A second observation wasmade on the toxicity of treatment on the caterpillars when they eat the leaves that hadbeen treated. The plant that was most effective was Elder Sambucus nigra followed byThymus vulgaris which reduced egg laying significantly. However, when also looking atthe toxicity of the treatment, the S. nigra had no effect on the caterpillars whereas only7% survived with the T. vulgaris at 5% concentration which was mixed with distilled water& Tween 20 (1%) as an emulsifier.

Göttig concludes that essential oils & plant extracts can act as a repellent causing asignificant reduction in egg laying by the female moths. This could be because the leavesof the treated plants have a slightly different optical property and texture due to the‘obvious fatty spray layer’. Whilst this didn’t affect the plant it did deter the moths fromlaying eggs and where caterpillars eat the treated leaves, they died in around twenty-four hrs.

Green frass balls(excrement from the

caterpillars) evident wherefeeding is taking place

# Frass Vials

In June 2017, researchers in Hungary published a paper inthe Journal of Pest Science (Vol.90 Issue 3 pp873-885)called ‘Synthetic blend of larval frass volatiles repeloviposition in the invasive box tree moth, Cydalima’ thatlooked at the ‘frass’, excrement produced by thecaterpillars when eating box leaves. [4] They noticed thatwhilst the caterpillars were feeding on leaves, the femalemoth didn’t lay eggs in the vicinity. They wondered whythis might be and looked at various possibilities, fromvisual cues to smells. Given the amount of excrement(frass) produced by the caterpillars, they decided to do achemical analysis using coupled gas chromatographic–electroantennographic detection and found threechemicals that when they did electrophysiological testingon the antenna of the male & female moths causedresponses. These three compounds, guaiacol, (±)-linalooland veratrole, were present for a couple of days after thecaterpillar had produced the frass. The next step was toproduce a synthetic version of this chemical mixture andput it in a bottle with a wick and place it near somepotted box plants. The results were impressive, reducingthe laying of eggs by around 75% compared to the controlenvironment. They concluded that the chemical mixturemay pave the way ‘to the development of successfulcontrol methods for the preservation of boxwoodpopulations in Europe.’ Now we have to hope that theirtrials can be reproduced on a large scale and that acompany invests in producing a commercial product assoon as possible.

Trichogramma

These parasitoids in the form of small wasps that lay their own eggs inside the egg sacks ofthe box moth eggs and when they hatch they eat the box moth eggs. These can be veryeffective, however, as they are a live product they have to be purchased and applied in atimely manner normally within 48hrs. The distribution method is often a biodegradablecardboard carrier that is hooked onto a branch inside a box plant. Low emergence ratesand a sex ratio unfavourable to females means they don’t reliably sustain their population –generally treatment lasts about two weeks before it should be repeated.

If the trichogramma are applied as soon as eggs have been laid and a minimum of twoconsecutive treatments are applied to the first set of eggs in the year it is possible toachieve 90% efficiency.

A lot of work has been carried out in France on producing products to release these naturalpredators, which are native to the Drôme region (though not in numbers high enough tocontrol the spread of the box moth). Bioline AgroSciences won first prize for innovation forits product Tricholine®Buxus. However, whilst effective, from an ease of use point of view,they require exact timing of orders, delivery and application as the trichogramma as it is aalive product.

Conclusion

There is a lot of research going on into box moth and it’s caterpillars, but it has spread farand wide so it isn’t going to be a simple matter to bring it under control. However, if a fewof the items being researched make it to becoming a commercial product it is possible toimagine a lure/vial combination that repels female moths from laying eggs whilst evenmore effectively attracting male moths into a trap and a simple organic spray that kills anycaterpillars that do emerge.

Chris Poole

EBTS UK© EBTS UK 2018

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Citations

[1] John R, Schumacher J (2013) Der Buchsbaum-Zünsler (Cydalima perspectalis) imGrenzach-Wyhlener Buchswald – Invasionschronik und Monitoringergebnisse. GesundePflanzen 65:1–6

[2] Citation Assessment of Forest Pests and Diseases in Native Boxwood Forests of GeorgiaFinal report by Dr. Iryna Matsiakh Forestry Department, Ukrainian National ForestryUniversity.

[3] Stefanie Gabriele Göttig, Dipl.-Biol., Technische Universität Darmstadt Development ofeco-friendly methods for monitoring and regulating the box tree pyralid, Cydalimaperspectalis (Lepidoptera: Crambidae), on invasive pest in ornamentals. 14.07.2017

[4] Molnár, B.P., Tóth, Z. & Kárpáti, Z. J Pest Sci (2017)

[5] USA Bacillus thuringiensis: A Cornerstone of Modern Agriculture, by Matthew Metz CRCPress, 24 Nov 2003

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